左联接未知列

Question

我在'on子句‘中得到了一个未知的列'assessment_assessment_type_lookup.assessment_type_fk’，下面的查询是这样的。表和列是正确的。

SELECT * FROM assessment
LEFT JOIN assessment_type 
ON assessment_type.assessment_type_pk = assessment_assessment_type_lookup.assessment_type_fk
LEFT JOIN assessment as ass
ON ass.assessment_pk = assessment_assessment_type_lookup.assessment_fk
LEFT JOIN unit_outcome
ON unit_outcome.unit_outcome_pk = unit_unit_outcome_lookup.unit_outcome_fk
LEFT JOIN unit
ON unit.unit_pk = unit_unit_outcome_lookup.unit_fk
LEFT JOIN unit_outcome as uo
ON uo.unit_outcome_pk = unit_outcome_assessment_lookup.unit_outcome_fk
LEFT JOIN assessment as ass2
ON ass2.assessment_pk = unit_outcome_assessment_lookup.assessment_fk
AND unit.unit_pk = '$unit_pk' GROUP BY assessment.assessment_pk

Answer 1

您正在尝试通过表assessment_type连接评估和，这是无法完成的。

如果希望连接2个表，则必须在其ON子句中使用这两个表。